1. Field of the Invention
The present invention relates to an optical lens assembly for image photographing, and more particularly to an optical lens assembly for image photographing consisting of four lens elements with a short total length for applying to electronic products.
2. Description of the Related Art
As advances in technology, current trends in the development of electronic products are primarily toward miniaturization, such as digital still cameras, web cameras or mobile phones. Users require a compact and low-cost optical lens assembly for image photographing, which also has a good aberration correction ability, high resolution, and high imagery quality at the same time.
In general, a conventional optical lens assembly of a compact electronic product comes with different designs, including the two-lens, three-lens, four-lens, and five-or-more lens designs. If the imagery quality is taken into considerations, the four-lens or five-lens optical lens assembly for image photographing is more advantageous in performance of good aberration correction and modulation transfer function (MTF) than others, wherein the four-lens compared to the five-lens has less lens and lower cost, and can be used in high pixel electronic products.
In various compact designs for the four-lens optical lens assemblies for image photographing, different combinations of positive or negative refractive powers are used in prior art as disclosed in U.S. Pat. Publication Nos. US2007/0058256, US2007/0070234, US2007/0242370 or US2008/0043346, etc.
In the compact products, such as digital cameras, web cameras, or mobile phone cameras, the optical lens assembly for image photographing requires a compact design, a short focal length and a good aberration correction. In disclosed prior art as U.S. Pat. or Publication Nos. U.S. Pat. Nos. 7,785,023, 7,692,877, 7,443,611, US2008/055742, US2009/0207506, European Pat. No. EP2090914, EP1821129, and WIPO Pat. No. WO201026691, designs having a combination of a first lens and second lens with positive refractive power and a fourth lens with negative refractive power are provided to meet requirements for good aberration correction and compact design. However, it is still necessary to shorten the total length of lenses in the optical lens assemblies for image photographing disclosed in these patents. Therefore, the present invention provides a feasible design for shortening the total length of the optical lens assembly for image photographing by a combination of refractive powers, concave surfaces and convex surfaces of the four lenses and providing a higher range of positive refractive powers for each lens before the fourth lens element with negative refractive power that will benefit to facilitate the compact design and good aberration correction ability, so as to reduce the total length of the optical system effectively and improve the imagery quality for applying to the electronic products.